The present invention relates to a control apparatus for controlling the displacement of a variable displacement compressor used in a refrigerant circuit of a vehicle air conditioner.
A typical variable displacement compressor includes a drive plate coupled to pistons. The drive plate is accommodated in a crank chamber. The pressure of the crank chamber is adjusted to alter the inclination angle of the drive plate, which varies the displacement of the compressor between the minimum displacement and the maximum displacement. The crank chamber pressure is adjusted by a control valve. Specifically, the opening degree of the control valve is adjusted based on a command from a controller.
If the discharge pressure is excessive in the refrigeration circuit, the pipes of the circuit receives excessive load. Therefore, when a discharge pressure sensor detects a pressure that is higher than a predetermined level, the controller adjusts the command signal to the control valve such that the compressor displacement is gradually decreased until the discharge pressure falls below the predetermined level (for example, in Japanese Unexamined Patent Publication No. 59-112156).
Compared to a case in which the displacement is quickly decreased, the invention of the publication, which gradually decreases the displacement, prevents the passenger from being disturbed by a sudden change in the cooling performance.
However, an excessively increased discharge pressure may not be quickly lowered according to a decrease in the compressor displacement. In this case, the displacement may be dropped to a value that is close to the minimum displacement. If the displacement is close to the minimum displacement, little refrigerant is supplied to the compressor from the external refrigerant circuit. That is, lubricant contained in the refrigerant is not sufficiently supplied to the compressor. Thus, the parts needing lubrication, such as sliding portions of the pistons and the cylinder bores, will be poorly lubricated.
Accordingly, it is an objective of the present invention to provide a control apparatus and a control method that reliably lubricate the sliding parts of a variable displacement compressor when lowering an excessive discharge pressure.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, an apparatus for controlling a variable displacement compressor used in a refrigerant circuit of an air conditioner is provided. The refrigerant circuit includes the compressor and an external circuit, which is connected to the compressor. The compressor compresses refrigerant sent from the external circuit and discharges the compressed refrigerant to the external circuit. The refrigerant circuit has a high pressure zone, which is exposed to the pressure of refrigerant that is compressed by the compressor. The compressor includes a drive shaft, which is rotated by an external drive source, and a tiltable drive plate, which is located in a crank chamber and converts rotation of the drive shaft to reciprocation of a piston. The drive plate changes its inclination angle in accordance with the pressure in the crank chamber. The drive plate changes the stroke of the piston according to its inclination angle thereby changing the displacement of the compressor. The apparatus includes a control valve, which adjusts the pressure in the crank chamber, a controller for controlling the control valve. The controller sends a command value that corresponds to cooling performance required for the refrigerant circuit to the control valve. The control valve operates to adjust its opening according to the sent command value. When the pressure in the high pressure zone is equal to or higher than a predetermined threshold value, the controller executes a limiting control for limiting the pressure in the high pressure zone. During the limiting control, the controller first gradually changes the command value, which is sent to the control valve, such that the displacement of the compressor is gradually decreased. Then, when the command value is equal to a predetermined reference value, the controller sends a command value that can minimize the displacement of the compressor to the control valve.
The present invention provides another apparatus for controlling a variable displacement compressor used in a refrigerant circuit of an air conditioner. The refrigerant circuit includes the compressor and an external circuit, which is connected to the compressor. The compressor compresses refrigerant sent from the external circuit and discharges the compressed refrigerant to the external circuit. The refrigerant circuit has a high pressure zone, which is exposed to the pressure of refrigerant that is compressed by the compressor. The compressor includes a drive shaft, which is coupled to an external drive source through a clutch mechanism, and a compression mechanism, which is actuated by the drive shaft to compress refrigerant and changes the displacement of the compressor. The apparatus includes an actuator for controlling the compression mechanism to change the displacement of the compressor, and a controller for controlling the actuator and the clutch mechanism. The controller sends a command value that corresponds to cooling performance required for the refrigerant circuit to the actuator. The actuator actuates the compression mechanism according to the sent command value. When the pressure in the high pressure zone is equal to or higher than a predetermined threshold value, the controller executes a limiting control for limiting the pressure in the high pressure zone. During the limiting control, the controller first gradually changes the command value, which is sent to the actuator, such that the displacement of the compressor is gradually decreased. Then, when the command value is equal to a predetermined reference value, the controller disconnects the drive shaft from the external drive source by using the clutch mechanism.
Further, the present invention provides a method for controlling a variable displacement compressor used in a refrigerant circuit of an air conditioner. The refrigerant circuit includes the compressor and an external circuit, which is connected to the compressor. The compressor compresses refrigerant sent from the external circuit and discharges the compressed refrigerant to the external circuit. The refrigerant circuit has a high pressure zone, which is exposed to the pressure of refrigerant that is compressed by the compressor. The compressor includes a tiltable drive plate, which is located in a crank chamber, the drive plate changes its inclination angle in accordance with the pressure in the crank chamber. The inclination angle of the drive plate determines the displacement of the compressor. The method includes adjusting the pressure in the crank chamber by a control valve, wherein the control valve operates according to a command value, which represents cooling performance required for the refrigerant circuit, and executing a limiting control for limiting the pressure in the high pressure zone when the pressure in the high pressure zone is equal to or higher than a predetermined threshold value, wherein, during the limiting control, the command value, which is sent to the control valve, is first gradually changed such that the displacement of the compressor is gradually decreased, and then, when the command value is equal to a predetermined reference value, a command value that can minimize the displacement of the compressor is sent to the control valve.
The present invention provides another method for controlling a variable displacement compressor used in a refrigerant circuit of an air conditioner. The refrigerant circuit includes the compressor and an external circuit, which is connected to the compressor. The compressor compresses refrigerant sent from the external circuit and discharges the compressed refrigerant to the external circuit. The refrigerant circuit has a high pressure zone, which is exposed to the pressure of refrigerant that is compressed by the compressor. The compressor includes a drive shaft, which is coupled to an external drive source through a clutch mechanism, and a compression mechanism, which is actuated by the drive shaft to compress refrigerant and changes the displacement of the compressor. The method includes controlling the compression mechanism by an actuator to change the displacement of the compressor, wherein the actuator operates according to a command value, which represents cooling performance required for the refrigerant circuit, and executing a limiting control for limiting the pressure in the high pressure zone when the pressure in the high pressure zone is equal to or higher than a predetermined threshold value, wherein, during the limiting control, the command value, which is sent to the actuator, is first gradually changed such that the displacement of the compressor is gradually decreased, and then, when the command value is equal to a predetermined reference value, the clutch mechanism disconnects the drive shaft from the external drive source.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.